The invention relates to a method for operating a hybrid drive device having an internal combustion engine and an electric machine which is operatively connectable or operatively connected to the internal combustion engine and which can be operated as a motor and as a generator, wherein in a normal operating mode a temperature of the electric machine is determined by means of a temperature sensor, and operation of the electric machine is permitted only when the temperature is less than a predefined maximum temperature. The invention further relates to a hybrid drive device.
The hybrid drive device is used, for example, for propelling a motor vehicle, i.e. to provide a torque for propelling the motor vehicle. The hybrid drive device includes a plurality of drive units, in particular at least two drive units, which are preferably of different types. For example, a first drive unit is configured as an internal combustion engine and a second drive unit is configured as an electric machine. The electric machine is operatively connectable or operatively connected to the internal combustion engine. In particular, a clutch is therefore provided between the electric machine and the internal combustion engine, by means of which an operative connection can be established between the drive units.
For example, it is provided that the electric machine is permanently connected to an output shaft of the hybrid drive device while the internal combustion engine can be disconnected by the clutch from the output shaft. Accordingly, provision can be made for the internal combustion engine and the electric machine to jointly provide, at least temporarily, the output torque of the hybrid drive device, which output torque is applied to the output shaft. Within the scope of the afore-described embodiment, the output torque can, however, also be generated only by the electric machine, i.e. without involvement of the internal combustion engine.
The electric machine can be operated both as a motor and as a generator. In both cases, it provides a torque that is positive in the case of the motor, i.e. it relates to an acceleration of the output shaft, whereas the torque is negative when being operated as a generator. In the latter case, the electric machine provides electrical energy, for example for an on-board electrical system of the motor vehicle.
The hybrid drive device preferably has at least one energy store, in particular a battery, in which the electrical energy can be temporarily stored. Likewise, provision may be made for the presence of a plurality of different on-board electrical systems, for example a high voltage on-board electrical system and a low voltage on-board electrical system, wherein a higher voltage is present than in the high voltage on-board electrical system than in the low voltage on-board electrical system. The high voltage on-board electrical system and the low voltage on-board electrical system can be electrically connected to one another via a voltage transformer. Preferably, the voltage transformer is used to feed or support the low voltage on-board electrical system with electrical energy from the high voltage on-board electrical system. Accordingly, the energy store is advantageously associated to the high voltage on-board electrical system and is operated with the voltage of the high voltage on-board electrical system.
In particular, when a large torque is provided in the case of a motor operation of the electric machine or a high electric power in the case of a generator operation, a substantial amount of heat is generated in the electric machine. This means that its temperature normally rises rapidly, with the temperature rise depending in particular on an ambient temperature. However, operation of the electric machine is preferred to be permitted only in a particular temperature range in order to prevent damage to the electric machine. In particular, at a high temperature of the electric machine, damage to a winding or other components of the electric machine can occur.
For this reason, the electric machine has the temperature sensor, by which its temperature can be determined. The temperature sensor is hereby in particular in heat transfer connection to particularly critical regions of the electric machine. Operation of the electric machine is now permitted at least in the normal operating mode only when the temperature, determined by the temperature sensor, is less than a predefined maximum temperature. The maximum temperature is hereby established in such a way that no failure of or damage to the electric machine is to be expected, even when the electric machine is operated for a long period at a temperature which corresponds to the maximum temperature. In addition or as an alternative, provision may be made to limit the torque, generated by the electric machine, to a maximum torque which is determined on the basis of the temperature ascertained by the temperature sensor.